A thought experiment, let's nickname it "Poisonous Gift":
Doesn't matter what cryptocurrency exactly, just assume the transaction ledger works like Bitcoin's.
Alice (wallet A) gets ransomwared by Rufus (wallet R), pays the rather large ransom (95 coins) but reports address R to the authorities, thus tainting wallet R.
Malcolm's money laundering gang (who has many unlinked but tainted wallets W,X,Y,Z and so forth, together tenthousands of coins) specialises in buying coins from well-known tainted wallets, moving all the tainted coins from wallet R into wallet M.
Security researcher and blogger Bob accepts donations:
Wallet B, linked to his real name, but comparatively little income/capital, only 5 coins.
Malcolm really doesn't like Bob's reporting, so wants to "poison" Bob's wallet, and get Bob in legal trouble, and is willing to spend the entirety of wallet M on it.
So he just sends all the funds from M to B.
Now Bob got 100 coins in his wallet, 95% directly tainted and linked to Rufus' ransomware campaign.
So when the authorities search for Rufus the ransomwarer, they see the money showing up on Bob's wallet, and might suspect him.
Not to mention exchanges might not accept Bob's wallet because of the "taint", thus blocking his much-needed income.